Wireless communication terminal and wireless communication method for clear channel allocation

ABSTRACT

The present invention relates to a wireless communication terminal and wireless communication method for clear channel assessment, and more particularly, to a wireless communication terminal and a wireless communication method for performing an efficient clear channel assessment for spatial reuse of a communication system. 
     For this, provided are a wireless communication terminal comprising: a transceiver configured to transmit and receive a wireless signal; and a processor configured to control an operation of the terminal, wherein the processor is configured to: perform a backoff procedure of a channel for data transmission, suspend the backoff procedure when a wireless signal having a signal strength higher than a predetermined first clear channel assessment (CCA) threshold is received through the channel, identify whether the received wireless signal is a wireless signal of the same basic service set (BSS) as the terminal, and determine whether to resume the backoff procedure based on a CCA threshold determined according to the identification result and a wireless communication method using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication terminal andwireless communication method for clear channel assessment, and moreparticularly, to a wireless communication terminal and a wirelesscommunication method for performing an efficient clear channelassessment for spatial reuse of a communication system.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high bitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

As described above, an object of the present invention is to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment.

In particular, an object of the present invention is to provide a methodfor efficiently transmitting data in an overlapped basic service set(BSS) environment.

Further, another object of the present invention is to increase atransmission opportunity and transmission rate of data by providing anefficient spatial reuse method in the overlapped BSS environment.

Further, another object of the present invention is to eliminate theunfairness problem of a legacy terminal that may occur when an adjustedCCA threshold is used for channel access.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminal,wherein the processor measures a signal strength of a wireless signal ofa specific channel received through the transceiver, and determineswhether the specific channel is busy based on the measured signalstrength and BSS identifier information of the wireless signal.

In this case, the processor may perform the determination based on clearchannel assessment (CCA) for the specific channel, and a CCA thresholdused for the CCA may be set to different levels according to whether theBSS identifier information of the wireless signal is the same as BSSidentifier information of the terminal.

Further, when the BSS identifier information of the wireless signal isthe same as BSS identifier information of the terminal, a first CCAthreshold may be used for the CCA and when the BSS identifierinformation of the wireless signal is different from BSS identifierinformation of the terminal, a second CCA threshold having a higherlevel than the first CCA threshold may be used for the CCA.

In addition, the processor may obtains at least one of legacy wirelessLAN information and non-legacy wireless LAN information by usingpreamble information of the received wireless signal, and may determinewhether the specific channel is busy based on the BSS identifierinformation of the wireless signal when the non-legacy wireless LANinformation is obtained from the wireless signal.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor for controlling an operation of the terminal,wherein the processor measures a signal strength of a wireless signal ofa specific channel received through the transceiver, obtains at leastone of legacy wireless LAN information and non-legacy wireless LANinformation by using preamble information of the received wirelesssignal, and determines whether the specific channel is busy based on BSSidentifier information of the wireless signal when the measured signalstrength is between a first clear channel assessment (CCA) threshold anda second CCA threshold and the non-legacy wireless LAN information isobtained from the wireless signal.

In this case, the BSS identifier information of the wireless signal mayrepresent abbreviated information of a BSS identifier for the wirelesssignal.

Further, the processor may determine whether the specific channel isbusy based on a result of comparing the BSS identifier information ofthe wireless signal and the BSS identifier information of the terminal.

In this case, the processor may determine that the specific channel isin an idle state when the BSS identifier information of the wirelesssignal is different from the BSS identifier information of the terminal.

Further, the processor may determine that the specific channel is in abusy state when the BSS identifier information of the wireless signal isthe same as the BSS identifier information of the terminal.

In addition, the wireless signal may include a first preamble for alegacy terminal and a second preamble for a non-legacy terminal, and theBSS identifier information of the wireless signal may be extracted fromthe second preamble of the wireless signal.

In addition, the wireless signal may include the first preamble for thelegacy terminal and the second preamble for the non-legacy terminal andthe first preamble may be configured to at least include a firstsubcarrier set for the legacy terminal, and when the first preamble isconfigured to additionally include a second subcarrier set differentfrom the first subcarrier set, the non-legacy wireless LAN informationmay be obtained from the second subcarrier set.

In this case, the BSS identifier information of the received wirelesssignal may be extracted from information on the second subcarrier set ofthe first preamble.

Further, the wireless signal may include the first preamble for thelegacy terminal and the second preamble for the non-legacy terminal, andwhether the wireless signal includes the non-legacy wireless LANinformation may be determined based on information on predetermined bitsof the first preamble.

In addition, the wireless signal may include the first preamble for thelegacy terminal and the second preamble for the non-legacy terminal, andthe BSS identifier information of the wireless signal may be extractedfrom the predetermined bit field of the first preamble.

In this case, a predetermined bit of the predetermined bit field mayrepresent whether the wireless signal includes the non-legacy wirelessLAN information, and when the predetermined bit represents that thewireless signal includes the non-legacy wireless LAN information, theBSS identifier information of the wireless signal may be extracted fromthe predetermined bit field.

In addition, the first preamble may be configured to at least includethe first subcarrier set for the legacy terminal, and when the firstpreamble is configured to additionally include the second subcarrier setdifferent from the first subcarrier set, the BSS identifier informationof the wireless signal may be extracted from the predetermined bitfield.

Next, the present invention provides a wireless communication terminalincluding: a transceiver for transmitting and receiving a wirelesssignal; and a processor controlling an operation of the terminal,wherein the processor performs a backoff procedure of a channel for datatransmission, suspends the backoff procedure when a wireless signalhaving a signal strength higher than a predetermined first clear channelassessment (CCA) threshold is received through the channel, identifieswhether the received wireless signal is a wireless signal of the samebasic service set (BSS) as the terminal, and determines whether toresume the backoff procedure based on a CCA threshold determinedaccording to the identification result.

In this case, the processor may determine whether to resume the backoffprocedure using a second CCA threshold higher than the first CCAthreshold when the wireless signal is determined to be a wireless signalof a different BSS with the terminal.

Further, the processor may determine that the channel is busy andcontinue to suspend the backoff procedure when the signal strength ofthe wireless signal is higher than the second CCA threshold.

Further, the processor may determine that the channel is idle and resumethe backoff procedure after a predetermined IFS time when the signalstrength of the wireless signal is lower than the second CCA threshold.

In addition, whether the received wireless signal is a wireless signalof the same BSS as the terminal may be identified based on BSS colorinformation or MAC address information extracted from the wirelesssignal.

In addition, the BSS color information may be abbreviated information ofa BSS identifier.

In addition, the wireless signal may be identified to be a wirelesssignal of the same BSS as the terminal when the wireless signal is aframe of a predetermined format not including the BSS identifierinformation.

In this case, the frame of the predetermined format may include a legacyCTS frame.

Further, the processor may determine that the channel is busy andcontinue to suspend the backoff procedure when the wireless signal isidentified to be a wireless signal of the same BSS as the terminal.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a wireless signal of a specific channel;measuring a signal strength of the received wireless signal; anddetermining whether the specific channel is busy based on the measuredsignal strength and BSS identifier information of the wireless signal.

Next, the present invention provides a wireless communication method ofa terminal including: receiving a wireless signal of a specific channel;measuring a signal strength of the received wireless signal; obtainingat least one of legacy wireless LAN information and non-legacy wirelessLAN information by using preamble information of the received wirelesssignal; and determining whether the specific channel is busy based onBSS identifier information of the wireless signal when the measuredsignal strength is between a first clear channel assessment (CCA)threshold and a second CCA threshold and the non-legacy wireless LANinformation is obtained from the wireless signal.

Next, the present invention provides a wireless communication method ofa terminal, the method comprising: performing a backoff procedure of achannel for data transmission; suspending the backoff procedure when awireless signal having a signal strength higher than a predeterminedfirst clear channel assessment (CCA) threshold is received through thechannel; identifying whether the received wireless signal is a wirelesssignal of the same basic service set (BSS) as the terminal; anddetermining whether to resume the backoff procedure based on a CCAthreshold determined according to the identification result.

Advantageous Effects

According to embodiments of the present invention, it can be efficientlydetermined whether a wireless signal received in an overlapped BSSenvironment is a wireless LAN signal of the same BSS and whether toadaptively use the corresponding channel can be decided based on thedetermination.

Further, according to another embodiment of the present invention, whenthe received wireless signal is a legacy wireless LAN signal from whichBSS identifier information is not extracted, whether the channel is in abusy state is determined according to a received signal strength of thecorresponding signal in a lump to minimize a time delay required toadditionally determine a BSS identifier of the legacy wireless LANsignal during a CCA process.

Further, according to another embodiment of the present invention, whena wireless LAN signal having the same BSS identifier information as thatof a terminal is received, an inequity problem in which different CCAthresholds are applied according to whether the corresponding wirelessLAN signal includes non-legacy wireless LAN information can be resolved.That is, CCA thresholds for a legacy signal and a non-legacy signal aresimilarly applied to the wireless LAN signal having the same BSSidentifier information as that of the terminal to maintain equity forchannel occupation between a legacy terminal and a non-legacy terminal.

According to yet another embodiment of the present invention, since atleast some of non-legacy wireless LAN information such as the BSSidentifier information can be obtained from a legacy preamble beforechecking a non-legacy preamble, CCA may be performed within a shortertime.

According to still another embodiment of the present invention, the BSSidentifier information is inserted into the legacy signal so that thenon-legacy terminals can apply the CCA threshold differently.

According to the embodiment of the present invention, when a pluralityof data frames are simultaneously transmitted, overlapping of thepreamble portions between each other is avoided, so that thetransmission success rate of each frame can be increased.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention.

FIG. 2 is a diagram illustrating a wireless LAN system according toanother embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

FIG. 6 is a diagram illustrating one embodiment of a wirelesscommunication scheme using a CCA technique.

FIG. 7 is a diagram illustrating one example of an overlapped BSSenvironment.

FIGS. 8 to 10 are diagrams illustrating various embodiments of a CCAmethod using BSS identifier information of a received wireless signal.

FIGS. 11 to 13 are diagrams illustrating another embodiment of a CCAmethod using whether to obtain non-legacy wireless LAN information froma received wireless signal and BSS identifier information.

FIG. 14 is a diagram illustrating a frame structure of a wireless LANsignal according to an embodiment of the present invention.

FIG. 15 is a diagram illustrating a method for representing BSSidentifier information according to an embodiment of the presentinvention.

FIG. 16 is a diagram illustrating an embodiment of a subcarrierconfiguration used in a legacy preamble of a wireless LAN signal.

FIG. 17 is a diagram illustrating an embodiment of a subcarrierconfiguration used in a non-legacy wireless LAN signal.

FIG. 18 is a diagram illustrating a method for representing non-legacywireless LAN information by using a predetermined bit field of thelegacy preamble.

FIG. 19 is a diagram illustrating an embodiment of the present inventionfor transmitting and receiving data between a non-legacy terminal and alegacy terminal.

FIG. 20 is a diagram illustrating a further embodiment of a CCA methodaccording to the present invention.

FIGS. 21 to 25 are diagrams illustrating various embodiments of thepresent invention in which a wireless communication terminal performsthe backoff procedure to transmit data.

BEST MODE

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-0170812 and 10-2014-0195876 filed in the KoreanIntellectual Property Office and the embodiments and mentioned itemsdescribed in the respective applications are included in the DetailedDescription of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of wirelesssignal transmission/reception of the station 100 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as wireless signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an interframespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber assigned to the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly assigned to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal is previously assigned. Meanwhile, each terminalattempts the access by performing the backoff procedure again in a nextcontention window interval and in this case, each terminal performs thebackoff procedure from slot time(s) which remained in the previouscontention window interval. By such a method, the respective terminalsthat perform the wireless LAN communication may avoid a mutual collisionfor a specific channel.

FIG. 6 is a diagram illustrating one embodiment of a wirelesscommunication scheme using a CCA technique.

In wireless communication, for instance, the wireless LAN communication,whether the channel is busy may be sensed through the CCA. In this case,the CCA methods including a signal detection (SD) method, an energydetection (ED) method, a correlation detection (CD) method, and the likemay be used.

First, the signal detection (CCA-SD) is a method that measures a signalstrength of a preamble of a wireless LAN (that is, 802.11) frame. Thismethod may stably detect the signal, but is disadvantageous in that themethod operates only in an initial part of a frame where the preamble ispresent. According to an embodiment, the signal detection may be used inthe CCA for a primary channel in a wideband wireless LAN. Next, theenergy detection (CCA-ED) is a method that senses energy of all signalsreceived with a specific threshold or more. This method may be used tosense a wireless signal in which the preamble is not normally sensed,for instance, signals such as Bluetooth, ZigBee, and the like. Further,the method may be used in the CCA for a secondary channel in which thesignal is not continuously tracked. Meanwhile, the correlation detection(CCA-CD) as a method that may sense a signal level even in the middle ofa wireless LAN frame uses that a wireless LAN signal has a periodicrepetition pattern of orthogonal frequency division multiplex (OFDM)signal. That is, the correlation detection method receives wireless LANdata for a predetermined time and thereafter, detects signal strengthsof the repetition patterns of an OFDM signal symbol.

According to the embodiment of the present invention, the access of theterminal to the channel may be controlled by using a predetermined CCAthreshold for each CCA method. In the embodiment of FIG. 6, a CCA-EDthreshold 10 represents a predetermined threshold in order to performthe energy detection and a CCA-SD threshold 30 represents apredetermined threshold in order to perform the signal detection.Further, receiving (RX) sensitivity 50 represents a minimum signalstrength at which the terminal may decode the wireless signal. Accordingto the embodiment, the RX sensitivity 50 may be set to a level which isthe same as or lower than the CCA-SD threshold 30 according to acapability and a configuration of the terminal. Further, the CCA-EDthreshold 10 may be set to a higher level than the CCA-SD threshold 30.For example, the CCA-ED threshold 10 and the CCA-SD threshold 30 may beset to −62 dBm and −82 dBm, respectively. However, the present inventionis not limited thereto and the CCA-ED threshold 10 and the CCA-SDthreshold 30 may be differently set according to whether the CCA-EDthreshold 10 and the CCA-SD threshold 30 are thresholds for the primarychannel, a bandwidth of a channel that performs the CCA, and the like.

According to the embodiment of FIG. 6, each terminal measures a receivedsignal strength indicator (RX RSSI) of the received wireless signal anddetermines a channel state based on a comparison between the measuredreceived signal strength and each set CCA threshold.

First, when a wireless signal 350 above the RX sensitivity 50, which isreceived in a specific channel has an RX RSSI of the CCA-SD threshold 30or less, it is determined that the corresponding channel is idle.Therefore, the received signal is not processed or protected in theterminal and each terminal may attempt the access to the correspondingchannel according to the method described in FIG. 5, and the like.

When a wireless LAN signal 330 having the RX RSSI of the CCA-SDthreshold 30 or more is received in a specific channel, it is determinedthat the corresponding channel is in a busy state. Accordingly, theterminal that receives the corresponding signal delays the access to thechannel. According to an embodiment, the terminal may determine whetherthe corresponding signal is the wireless LAN signal by using a signalpattern of a preamble part of the received wireless signal. According tothe embodiment of FIG. 6, even in case that a wireless LAN signal ofother BSS is received in addition to a wireless LAN signal of BSS whichis the same with the corresponding terminal, each terminal determinesthat the channel is in the busy state.

Meanwhile, when a wireless signal 310 having the RX RSSI of the CCA-EDthreshold 10 or more is received in a specific channel, it is determinedthat the corresponding channel is in the busy state. In case thatanother type of wireless signal (other than the wireless LAN signal) isreceived as well, the terminal determines that the corresponding channelis in the busy state, if the RX RSSI of the corresponding signal is theCCA-ED threshold 10 or more. Accordingly, the terminal that receives thecorresponding signal delays the access to the channel.

FIG. 7 illustrates one example of an overlapping BSS (OBSS) environment.In FIG. 7, in BSS-1 operated by AP-1, station 1 (STA-1) and station 2(STA-2) are associated with AP-1 and in BSS-2 operated by AP-2, station3 (STA-3) and station 4 (STA-4) are associated with AP-2. In theoverlapping BSS environment of FIG. 7, communication coverages of BSS-1and BSS-2 at least partially overlap with each other.

As illustrated in FIG. 7, when STA-3 transmits upload data to AP-2,STA-3 may continuously interfere with STA-2 of BSS-1 positioned adjacentthereto. In this case, interference which occurs while BSS-1 and BSS-2use the same frequency band (for example, 2.4 GHz, 5 GHz, or the like)and the same primary channel is referred to as co-channel interference(CCI). Further, interference which occurs while BSS-1 and BSS-2 use anadjacent primary channel is referred to as adjacent channel interference(ACI). The CCI or ACI may be received with a higher signal strength thanthe CCA threshold (e.g. CCA SD threshold) of STA-2 according to adistance between STA-2 and STA-3. When the interference is received bySTA-2 with the higher strength than the CCA threshold, STA-2 recognizesthat the corresponding channel is in the busy state to delaytransmission of the upload data to AP-1. However, since STA-2 and STA-3are stations that belong to different BSSs, when the CCA threshold ofSTA-2 increases, STA-2 and STA-3 may simultaneously upload to AP-1 andAP-2, respectively, thereby achieving an effect of spatial reuse.

Meanwhile, in FIG. 7, the transmission of the upload data by STA-3 inBSS-2 interferes even in STA-4 that belongs to the same BSS-2. In thiscase, when the CCA threshold of STA-4 increases similarly to STA-2,STA-3 and STA-4 that belong to the same BSS simultaneously transmit theupload data to AP-2, and as a result, a collision may occur. Therefore,in order to increase the CCA threshold for predetermined interference,it is needed to determine whether the corresponding interference iscaused by signals that belong to the same BSS or signals that belong todifferent BSSs. To this end, each terminal needs to verify a BSSidentifier of the received wireless LAN signal or other types ofinformation to distinguish the BSS. Further, it is preferable that theBSS information is verified within a short time while the CCA process isperformed.

FIGS. 8 to 13 are diagrams illustrating various embodiments of the CCAmethod according to the present invention. In the embodiments of FIGS. 8to 13, an area marked with a shade indicates a wireless signal which isreceived but disregarded, that is, not protected by the terminal. Inother words, when the wireless signal corresponding to the area markedwith the shade is received, the terminal determines that thecorresponding channel is in the idle state. Meanwhile, when a wirelesssignal corresponding to an area not marked with the shade is received,the terminal determines that the corresponding channel is in the busystate. In this case, the RX sensitivity may be set to the level which isthe same as or lower than the CCA-SD threshold according to thecapability and the configuration of the terminal. Further, the CCA-EDthreshold may be set to the higher level than the CCA-SD threshold.Individual processes described in FIG. 5 may be performed based on aresult of determining whether the channel is busy in each embodiment tobe described below.

In each of the embodiments of FIGS. 8 to 10, the terminal may measurethe RX RSSI of the received wireless signal and determine whether thecorresponding signal is the wireless LAN signal. When the receivedsignal is the wireless LAN signal having the BSS identifier informationaccording to various embodiments to be described below, the terminal mayextract the BSS identifier information from the corresponding signal anddetermine whether the extracted BSS identifier information is the sameas the BSS identifier information of the corresponding terminal.

First, according to the embodiment of FIG. 8, the CCA threshold for thecorresponding signal may be decided based on whether the receivedwireless signal is the wireless LAN signal having the BSS identifierinformation which is the same as the BSS identifier information of theterminal. In the embodiment of the present invention, the BSS identifierinformation of the terminal is BSS identifier information assigned tothe corresponding terminal and may represent, when the correspondingterminal is a non-AP STA, BSS identifier information of an AP which thecorresponding terminal is associated with or intends to be associatedwith. In this case, the terminal may receive the BSS identifierinformation from the AP and the received BSS identifier information maybe stored in the corresponding terminal.

Referring to FIG. 8, when a received wireless signal of a specificchannel is the wireless LAN signal having an RX RSSI of the RXsensitivity 50 or more and the CCA-SD threshold 30 or less, whether thechannel is busy is determined based on whether the corresponding signalis the wireless LAN signal having the same BSS identifier information asthat of the terminal. When the BSS identifier information extracted fromthe wireless signal is different from the BSS identifier information ofthe terminal (that is, in the case of OBSS wireless LAN signal 452), itis determined that the corresponding channel is in the idle state.However, when the BSS identifier information extracted from the wirelesssignal is the same as the BSS identifier information of the terminal(that is, in the case of MYBSS wireless LAN signal 454), it isdetermined that the corresponding channel is in the busy state.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 430 having the RX RSSI between the CCA-SDthreshold 30 and the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state. In this case, even in thecase where the corresponding signal is a wireless LAN signal havingdifferent BSS identifier information from that of the terminal inaddition to the case where the corresponding signal is the wireless LANsignal having the same BSS identifier information as that of theterminal, the terminal that receives the wireless LAN signal 430determines that the channel where the corresponding signal is receivedis in the busy state.

During the energy detection process, when the wireless signal of thespecific channel, which is received by the terminal is a wireless signal410 having the RX RSSI of the CCA-ED threshold 10 or more, it isdetermined that the corresponding channel is in the busy state. Asdescribed above, in case that another type of wireless signal (otherthan the wireless LAN signal) is received as well, the terminaldetermines that the corresponding channel is in the busy state, if theRX RSSI of the wireless signal is the CCA-ED threshold 10 or more.

As such, according to the embodiment of FIG. 8, the CCA thresholdapplied to the wireless LAN signal having the same BSS identifierinformation as that of the terminal may have a different level from theCCA threshold applied to the wireless LAN signal having the differentBSS identifier information from that of the terminal. According to anembodiment, the CCA threshold applied to the wireless LAN signal havingthe different BSS identifier information from that of the terminal isset to a higher level than the CCA threshold applied to the wireless LANsignal having the same BSS identifier information as that of theterminal. According to the embodiment of FIG. 8, as the CCA thresholdfor the wireless LAN signal having the different BSS identifierinformation from that of the terminal, the predetermined CCA-SDthreshold 30 may be adopted and as the CCA threshold for the wirelessLAN signal having the same BSS identifier information as that of theterminal, the level of the RX sensitivity 50 of the terminal may beadopted.

FIGS. 9 and 10 illustrate another embodiment of the CCA method using theBSS identifier information. In the embodiments of FIGS. 9 and 10,duplicative description of parts, which are the same as or correspond tothe embodiment of FIG. 8, will be omitted.

First, according to the embodiment of FIG. 9, the CCA threshold for thecorresponding signal may be decided based on whether the receivedwireless signal is the wireless LAN signal having the BSS identifierinformation which is the same as the BSS identifier information of theterminal.

Referring to FIG. 9, when the RX RSSI of a received wireless signal of aspecific channel is the RX sensitivity 50 or more and a first CCA-SDthreshold 40 or less, it is determined that the corresponding channel isin the idle state. In this case, both in the case where the receivedsignal is a wireless LAN signal 454 having the same BSS identifierinformation as that of the terminal and in the case where the receivedsignal is a wireless LAN signal 452 having the different BSS identifierinformation from that of the terminal, the terminal determines that thechannel where the corresponding signal is received is in the idle state.

However, when the received wireless signal of the specific channel isthe wireless LAN signal having the RX RSSI between the first CCA-SDthreshold 40 and a second CCA-SD threshold 20, whether the channel isbusy is determined based on whether the corresponding signal is thewireless LAN signal having the same BSS identifier information as thatof the terminal. When the BSS identifier information extracted from thewireless signal is different from the BSS identifier information of theterminal (that is, in the case of OBSS wireless LAN signal 442), it isdetermined that the corresponding channel is in the idle state. However,when the BSS identifier information extracted from the wireless signalis the same as the BSS identifier information of the terminal (that is,in the case of MYBSS wireless LAN signal 444), it is determined that thecorresponding channel is in the busy state. In the embodiment of FIG. 9,the second CCA-SD threshold 20 which is used to perform the signaldetection for the wireless LAN signal having the different BSSidentifier information from that of the terminal may be set to a levelwhich is larger than the first CCA-SD threshold 40 and equal to orsmaller than the CCA-ED threshold.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 420 having an RX RSSI between the second CCA-SDthreshold 20 and the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state. In this case, even in thecase where the corresponding signal is a wireless LAN signal havingdifferent BSS identifier information from that of the terminal inaddition to the case where the corresponding signal is the wireless LANsignal having the same BSS identifier information as that of theterminal, the terminal that receives the wireless LAN signal 420determines that the channel where the corresponding signal is receivedis in the busy state.

During the energy detection process, when the received wireless signalof the specific channel by the terminal is a wireless signal 410 havingthe RX RSSI of the CCA-ED threshold 10 or more, it is determined thatthe corresponding channel is in the busy state. As described above, incase that another type of wireless signal (other than the wireless LANsignal) is received as well, the terminal determines that thecorresponding channel is in the busy state, if the RX RSSI of thewireless signal is the CCA-ED threshold 10 or more.

As such, according to the embodiment of FIG. 9, the CCA thresholdapplied to the wireless LAN signal having the same BSS identifierinformation as that of the terminal may have a different level from theCCA threshold applied to the wireless LAN signal having the differentBSS identifier information from that of the terminal. That is, as theCCA threshold for the wireless LAN signal having the same BSS identifierinformation as that of the terminal, the predetermined first CCA-SDthreshold 40 may be adopted and as the CCA threshold for the wirelessLAN signal having the different BSS identifier information from that ofthe terminal, the predetermined second CCA-SD threshold 20 may beadopted. Herein, the second CCA-SD threshold 20 may be set to a levelwhich is higher than the first CCA-SD threshold 40 and equal to or lowerthan the CCA-ED threshold.

Next, according to the embodiment of FIG. 10, when the RX RSSI of areceived wireless signal of a specific channel is the RX sensitivity 50or more, the signal detection may be performed based on whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal.

During the signal detection process, when the RX RSSI of the wirelesssignal received by the terminal is the RX sensitivity 50 or more and thewireless signal is a wireless LAN signal 453 having the same BSSidentifier information as that of the terminal, it is determined thatthe corresponding channel is in the busy state. However, when the RXRSSI of the received wireless signal is the RX sensitivity 50 or moreand the wireless signal is a wireless LAN signal 451 having differentBSS identifier information from that of the terminal, it is determinedthat the corresponding channel is in the idle state.

Meanwhile, during the energy detection process, when the wireless signalreceived by the terminal is the wireless signal 410 having the RX RSSIof the CCA-ED threshold 10 or more, it is determined that thecorresponding channel is in the busy state. The terminal determines thatthe corresponding channel is in the busy state regardless of whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal and furthermore,regardless of whether the corresponding signal is the wireless LANsignal. Therefore, when the wireless LAN signal having the different BSSidentifier information from that of the terminal is received at a levelhigher than the CCA-ED threshold 10, it is determined that thecorresponding channel is in the busy state by the energy detectionprocess.

As such, according to the embodiment of FIG. 10, the terminal maydetermine whether the channel is busy based on whether the receivedwireless signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal without using aseparately set CCA-SD threshold during the signal detection process.However, the terminal may avoid a collision with the wireless LAN signalhaving the different BSS identifier information from that of theterminal by using the predetermined CCA-ED threshold 10 for the energydetection.

FIGS. 11 to 13 are diagrams illustrating yet another embodiment of a CCAmethod using whether to obtain non-legacy wireless LAN information andBSS identifier information. In each embodiment of FIGS. 11 to 13, theterminal may measure the RX RSSI of the received wireless signal anddetermine whether the corresponding signal is the wireless LAN signal.When the received signal is the wireless LAN signal having the BSSidentifier information according to various embodiments to be describedbelow, the terminal may extract the BSS identifier information from thecorresponding signal and determine whether the extracted BSS identifierinformation is the same as the BSS identifier information of thecorresponding terminal.

Moreover, the terminal may obtain at least one of the legacy wirelessLAN information and the non-legacy wireless LAN information from thereceived wireless signal. As a result, the terminal may determinewhether the received wireless signal is a signal including only thelegacy wireless LAN information or a signal including both the legacywireless LAN information and the non-legacy wireless LAN information.According to an embodiment, the terminal may obtain at least one of thelegacy wireless LAN information and the non-legacy wireless LANinformation by using preamble information of the received wirelesssignal. The BSS identifier information of the wireless signal may beextracted from the non-legacy wireless LAN information when thenon-legacy wireless LAN information is obtained from the correspondingsignal. However, the present invention is not limited thereto andaccording to various embodiments described below the BSS identifierinformation of the wireless signal may be also extracted from the legacywireless LAN information. According to an embodiment of the presentinvention, the BSS identifier information which is referred to forexecuting the CCA is included in the non-legacy wireless LANinformation, while the non-legacy wireless LAN information may not beincluded in the received wireless signal. That is, when the receivedwireless signal does not include the BSS identifier information which isreferred to for executing the CCA according to the embodiment of thepresent invention, the BSS identifier information may not be extractedfrom the corresponding signal. In this case, the BSS identifierinformation of the corresponding signal for executing the CCA may be setto a predetermined value. In the embodiments of FIGS. 11 to 13,duplicative description of parts, which are the same as or correspond tothe aforementioned embodiments, will be omitted.

First, referring to FIG. 11, when a received wireless signal of aspecific channel is the wireless LAN signal having the RX RSSI of the RXsensitivity 50 or more and the first CCA-SD threshold 40 or less,whether the channel is busy is determined based on whether thecorresponding signal is the wireless LAN signal having the same BSSidentifier information as that of the terminal.

When the BSS identifier information extracted from the wireless signalis different from the BSS identifier information of the terminal (thatis, in the case of OBSS wireless LAN signal), it is determined that thecorresponding channel is in the idle state. In this case, the OBSSwireless LAN signal 552 may be divided into an OBSS non-legacy wirelessLAN signal in which the non-legacy wireless LAN information may beobtained from the corresponding signal and an OBSS legacy wireless LANsignal in which the non-legacy wireless LAN information is not obtainedfrom the corresponding signal. The terminal determines that thecorresponding channel is in the idle state both in the case where theOBSS non-legacy wireless LAN signal is received and in the case wherethe OBSS legacy wireless LAN signal is received.

On the contrary, when the BSS identifier information extracted from thewireless signal is the same as the BSS identifier information of theterminal (that is, in the case of MYBSS wireless LAN signal), it isdetermined that the corresponding channel is in the busy state.Similarly, the MYBSS wireless signal may be divided into a MYBSSnon-legacy wireless LAN signal 558 in which the non-legacy wireless LANinformation may be obtained from the corresponding signal and an MYBSSlegacy wireless LAN signal 556 in which the non-legacy wireless LANinformation is not obtained from the corresponding signal. The terminaldetermines that the corresponding channel is in the busy state both inthe case where the MYBSS non-legacy wireless LAN signal 558 is receivedand in the case where the MYBSS legacy wireless LAN signal 556 isreceived.

Meanwhile, when the received wireless signal of the specific channel isthe wireless LAN signal having the RX RSSI between the first CCA-SDthreshold 40 and the second CCA-SD threshold 20, whether the channel isbusy is determined based on whether the corresponding signal includesthe non-legacy wireless LAN information and whether the correspondingsignal has the same BSS identifier information as that of the terminal.According to an embodiment, the first CCA-SD threshold 40 may be set tothe same level as the CCA-SD threshold applied to the legacy terminaland the second CCA-SD threshold 20 may be set to a higher level than thefirst CCA-SD threshold 40 and equal to or lower than the CCA-EDthreshold.

When the non-legacy wireless LAN information is obtained from thewireless signal and the BSS identifier information of the correspondingsignal is different from the BSS identifier information of the terminal(that is, in the case of non-legacy OBSS signal 542), it is determinedthat the corresponding channel is in the idle state. However, in othercases, when the non-legacy wireless LAN information is not obtained fromthe wireless signal (that is, a legacy signal) or the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal (that is, a MYBSS signal), it isdetermined that the corresponding channel is in the busy state. In moredetail, the case where it is determined that the channel is in the busystate includes i) a case where the non-legacy wireless LAN informationis not obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is different from the BSSidentifier information of the terminal (that is, in the case of legacyOBSS signal 544), ii) a case where the non-legacy wireless LANinformation is not obtained from the wireless signal and the BSSidentifier information of the corresponding signal is the same as theBSS identifier information of the terminal (that is, in the case oflegacy MYBSS signal 546), and iii) a case where the non-legacy wirelessLAN information is obtained from the wireless signal and the BSSidentifier information of the corresponding signal is the same as theBSS identifier information of the terminal (that is, in the case ofnon-legacy MYBSS signal 548).

That is, when the non-legacy wireless LAN information is not obtainedfrom the wireless signal, it is determined that the correspondingchannel is in the busy state, but when the non-legacy wireless LANinformation is obtained from the wireless signal, whether the channel isbusy is determined based on whether the BSS identifier information ofthe corresponding signal is the same as the BSS identifier informationof the terminal. Therefore, according to the embodiment of the presentinvention, when the non-legacy wireless LAN information is obtained fromthe wireless signal, whether the corresponding channel is busy may bedetermined based on the BSS identifier information of the wirelesssignal. According to an embodiment, when the non-legacy wireless LANinformation is not obtained from the wireless signal, the BSS identifierinformation which is referred to for executing the CCA of the presentinvention may not be extracted from the corresponding signal. In thiscase, the terminal may determine that the channel is in the busy stateregardless of whether the BSS identifier information is extracted fromthe corresponding signal.

The signal detection process may be performed by referring to thepreamble of the received wireless signal. According to an embodiment,when it is determined that the channel is in the busy state during thesignal detection process, even though the RX RSSI decreases to the firstCCA-SD threshold 40 or less while receiving the wireless signal which isbeing protected, the terminal may not access the channel during a frametransmission time of the wireless signal.

Meanwhile, when the received wireless signal of the specific channel isa wireless LAN signal 520 between the second CCA-SD threshold 20 and theCCA-ED threshold 10, it is determined that the corresponding channel isin the busy state. In this case, the terminal that receives the wirelessLAN signal 520 determines that a channel where the corresponding signalis received is in the busy state regardless of whether the non-legacywireless LAN information is obtained from the corresponding signal andfurthermore, regardless of whether the corresponding signal is thewireless LAN signal having the same BSS identifier information as thatof the terminal.

During the energy detection process, when the received wireless signalof the specific channel by the terminal is a wireless signal 510 of theCCA-ED threshold 10 or more, it is determined that the correspondingchannel is in the busy state. As described above, in case that anothertype of wireless signal (other than the wireless LAN signal) is receivedas well, the terminal determines that the corresponding channel is inthe busy state, if the RX RSSI of the wireless signal is the CCA-EDthreshold 10 or more.

Next, according to the embodiment of FIG. 12, when a received wirelesssignal of a specific channel is the wireless LAN signal having the RXsensitivity 50 or more and the RX RSSI of the first CCA-SD threshold 40or less, whether the channel is busy is determined based on whether thecorresponding signal includes the non-legacy wireless LAN informationand whether the corresponding signal has the same BSS identifierinformation as that of the terminal.

When the non-legacy wireless LAN information is obtained from thewireless signal and the BSS identifier information of the correspondingsignal is the same as the BSS identifier information of the terminal(that is, in the case of non-legacy MYBSS signal 558), it is determinedthat the corresponding channel is in the busy state. However, in othercases, when the BSS identifier information of the wireless signal isdifferent from the BSS identifier information of the terminal (that is,OBSS signal) or the non-legacy wireless LAN information is not obtainedfrom the corresponding signal (that is, legacy signal), it is determinedthat the corresponding channel is in the idle state. In more detail, thecase where it is determined that the channel is in the idle stateincludes i) a case where the non-legacy wireless LAN information isobtained from the wireless signal and the BSS identifier information ofthe corresponding signal is different from the BSS identifierinformation of the terminal (that is, in the case of non-legacy OBSSsignal 552), ii) a case where the non-legacy wireless LAN information isnot obtained from the wireless signal and the BSS identifier informationof the corresponding signal is different from the BSS identifierinformation of the terminal (that is, in the case of legacy BSS signal554), and iii) a case where the non-legacy wireless LAN information isnot obtained from the wireless signal and the BSS identifier informationof the corresponding signal is the same as the BSS identifierinformation of the terminal (that is, in the case of legacy MYBSS signal556).

That is, when the non-legacy wireless LAN information is not obtainedfrom the wireless signal, it is determined that the correspondingchannel is in the idle state, but when the non-legacy wireless LANinformation is obtained from the wireless signal, whether the channel isbusy is determined based on whether the BSS identifier information ofthe corresponding signal is the same as the BSS identifier informationof the terminal. According to the embodiment of FIG. 12, when thenon-legacy wireless LAN information is obtained from the wireless signaland the BSS identifier information of the corresponding signal isdifferent from the BSS identifier information of the terminal, apredetermined CCA threshold 20 may be used for the CCA of thecorresponding channel. However, when the non-legacy wireless LANinformation is obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal, in the case where thecorresponding signal has the RX RSSI of the RX sensitivity 50 or more,it may be determined that the corresponding channel is in the busy statewithout setting a separate CCA threshold. According to an embodiment,when the non-legacy wireless LAN information is not obtained from thewireless signal, the BSS identifier information which is referred to forexecuting the CCA of the present invention may not be extracted from thecorresponding signal. In this case, the terminal may determine that thechannel is in the idle state regardless of whether the BSS identifierinformation is extracted from the corresponding signal.

According to the embodiment of FIG. 12, even though the BSS identifierinformation which is referred to for executing the CCA is included inthe non-legacy wireless LAN information and the received wireless LANsignal does not include the non-legacy wireless LAN information, the CCAmay be efficiently executed. That is, when the received wireless signalis the legacy wireless LAN signal from which the BSS identifierinformation is not extracted, it is determined that the correspondingchannel is in the idle state or the busy state in a lump according tothe RX RSSI of the corresponding signal to minimize a time delayrequired to determine whether the BSS identifier of the legacy wirelessLAN signal is actually the same as the BSS identifier of the terminal.That is, only when the received wireless signal is the non-legacywireless LAN signal, the terminal additionally verifies the BSSidentifier information to determine whether the channel is in theidle/busy state.

Next, according to the embodiment of FIG. 13, when the RX RSSI of areceived wireless signal of a specific channel is the RX sensitivity 50or more and the first CCA-SD threshold 40 or less, it is determined thatthe corresponding channel is in the idle state. In this case, theterminal determines that the corresponding channel is in the idle stateregardless of whether the received signal includes the non-legacywireless LAN information and whether the received signal has the sameBSS identifier information as that of the terminal. Further, accordingto the embodiment of FIG. 13, when the non-legacy wireless LANinformation is obtained from the wireless signal and the BSS identifierinformation of the corresponding signal is the same as the BSSidentifier information of the terminal, a first CCA threshold may beused for the CCA of the corresponding channel. However, when thenon-legacy wireless LAN information is obtained from the wireless signaland the BSS identifier information of the corresponding signal isdifferent from the BSS identifier information of the terminal, a secondCCA threshold having a higher level than the first CCA threshold may beused for the CCA of the corresponding channel.

According to the embodiment of FIG. 13, when the wireless LAN signalhaving the same BSS identifier information as that of the terminal isreceived, a problem of unfairness in that different CCA thresholds areapplied according to whether the corresponding wireless LAN signalincludes the non-legacy wireless LAN information may be resolved. Thatis, CCA thresholds for the legacy MYBSS signal and the non-legacy MYBSSsignal are similarly applied to maintain fairness for channel occupationbetween a legacy terminal and a non-legacy terminal.

Meanwhile, in the embodiments of FIGS. 12 and 13, when the wirelesssignal having the RX RSSI of the first CCA-SD threshold 40 or more isreceived, a CCA process may be performed similarly to the embodiment ofFIG. 11.

FIG. 14 is a diagram illustrating a frame structure of a wireless LANsignal according to an embodiment of the present invention. Referring toFIG. 14, the wireless LAN signal according to the embodiment of thepresent invention may include a legacy preamble 710 for a legacyterminal (e.g. a terminal such as 802.11a/g, or the like) and anon-legacy preamble 720 for a non-legacy terminal (e.g. a terminal of802.11ax). First, the legacy preamble 710 may include legacy wirelessLAN information which the legacy terminal is able to decode, forinstance, L-STF, L-LTF, L-SIG fields, and the like. Next, the non-legacypreamble 720 may include non-legacy wireless LAN information which onlythe non-legacy terminal is able to decode and the non-legacy wirelessLAN information may not be decoded by the legacy terminal. Meanwhile,the legacy preamble 710 may include at least some of the non-legacywireless LAN information which the non-legacy terminal is able to decodeaccording to the embodiment. Moreover, the non-legacy preamble 720 mayinclude at least one field of the legacy preamble 710, for instance,repeated information of a part or the entirety of the L-SIG field.

According to an embodiment of the present invention, the BSS identifierinformation which is referred to for executing the CCA may be includedin the non-legacy preamble 720 as the non-legacy wireless LANinformation. In this case, the BSS identifier information may beextracted from a predetermined bit filed of the non-legacy preamble 720.Meanwhile, according to another embodiment of the present invention, theBSS identifier information may be extracted from additional informationof the legacy preamble 710. For example, the legacy preamble 710 mayinclude the non-legacy wireless LAN information through an additionalsubcarrier set, and the like as described below and the BSS identifierinformation may be obtained from the non-legacy wireless LAN informationincluded in the legacy preamble 710. According to yet another embodimentof the present invention, the BSS identifier information may beextracted from a predetermined bit field of the legacy preamble 710. Inthis case, the predetermined bit field of the legacy preamble 710 may bea bit field set for the legacy terminal and a value of the correspondingbit field may be used as the BSS identifier information under a specificcondition as described below.

FIG. 15 illustrates a method for representing the BSS identifierinformation according to an embodiment of the present invention.According to the embodiment of the present invention, the BSS identifierinformation may be represented as a predetermined bit filed of thenon-legacy preamble 720 of FIG. 14. According to an embodiment of thepresent invention, the BSS identifier information may be abbreviatedinformation of a BSS identifier assigned to each BSS and may beinformation having smaller bits than the actual BSS identifier. Forexample, when the BSS identifier is represented as information of 24bits in a specific wireless LAN system, the BSS identifier informationmay be represented as a bit filed having a predetermined length in therange of 1 bit to 23 bits. In the preset invention, the BSS identifierinformation is information acquired by classifying the actual BSSidentifier into a predetermined category and may be named even as a BSScolor. A method for obtaining a BSS color abbreviated from the BSSidentifier includes a method using a combination of bit values at apredetermined location of the BSS identifier, a method using a resultvalue acquired by applying a predetermined Hash function to the BSSidentifier, and the like.

FIG. 15 as an embodiment thereof illustrates a result of acquiring theBSS color by using last 3 bit values of the BSS identifier. As such, theBSS color may be included in the preamble of the wireless LAN signal asinformation of a smaller amount than the actual BSS identifier, and as aresult, each terminal may efficiently determine whether the receivedwireless LAN signal is a signal having the same BSS identifier as thecorresponding terminal within a short time. The BSS identifierinformation may be represented as a predetermined bit of the non-legacypreamble.

Meanwhile, according to an embodiment of the present invention, thenon-legacy preamble 720 may include the repeated L-SIG field and therepeated L-SIG field may be configured to have at least the some bitsidentical with the L-SIG field of the legacy preamble 710. In this case,the bits different from the L-SIG field of the legacy preamble 710 amongthe bits of the repeated L-SIG field may represent the BSS identifierinformation, bandwidth information of the system, non-legacy wirelessLAN system information, channel information, and the like.

According to an additional embodiment of the present invention,additional information may be transmitted through a modulation methodapplied to the repeated L-SIG field. That is, the repeated L-SIG fieldmay be represented as the same modulation value as the L-SIG field ofthe legacy preamble 710 or otherwise expressed as a counter modulationvalue. Herein, the counter modulation value may be represented through aphase shift between modulation symbols transmitted to the L-SIG of thelegacy preamble 710 and modulation symbols of the repeated L-SIG and theadditional information may be transmitted through a phase shift amount.In detail, when the L-SIG of the legacy preamble 710 and the repeatedL-SIG are multiplied by (1, 1) to be transmitted, the symbols of bothfields have the same phase and when the L-SIG of the legacy preamble 710and the repeated L-SIG are multiplied by (1, −1) to be transmitted, aphase shift of 180° occurs between the symbols of the repeated L-SIG andthe symbols of the legacy preamble 710. In this case, specific flaginformation for the non-legacy wireless LAN information may bedetermined according to whether the repeated L-SIG field is representedas the same modulation value as the L-SIG field of the legacy preamble710, for example, whether a SIG-A field of the non-legacy preamble has avariable length, whether a SIG-B field is included in the non-legacypreamble, whether a specific bit field of the non-legacy preamble(alternatively, legacy preamble) represents the BSS identifierinformation, and the like may be determined.

FIGS. 16 and 17 as another embodiment of the present inventionillustrate a method for obtaining the non-legacy wireless LANinformation by using an additional subcarrier set of the wireless LANsignal.

First, FIG. 16 illustrates an embodiment of a subcarrier configurationused in the legacy preamble of the wireless LAN signal. According to anembodiment of the present invention, the subcarrier set of the legacypreamble of the non-legacy wireless LAN signal may be configuredequivalent to the subcarrier set of the legacy wireless LAN signal. Thatis, the subcarrier set of the legacy preamble may be constituted by atotal of 52 subcarrier including 4 pilot subcarriers and 48 datasubcarriers in a bandwidth of 20 MHz. In this case, when numbers ofrespective subcarriers are set to −26, −25, . . . , −2, −1, 1, 2, . . ., 25, and 26, subcarriers having numbers of −21, −7, 7, and 21 are usedas the pilot subcarriers and subcarriers of the residual numbers areused as the data subcarriers. Such a basic configuration of thesubcarrier is required to maintain mutual compatibility in anenvironment in which the legacy wireless LAN system (e.g. 802.11 a/g)and the non-legacy wireless LAN system (e.g. 802.11 ax, or the like)coexist. That is, the legacy preamble of the non-legacy wireless LANsignal as well as the legacy wireless LAN signal has the subcarrierconfiguration illustrated in FIG. 16 to provide backward compatibilityto the legacy terminal.

FIG. 17 illustrates an embodiment of the subcarrier configuration usedin the non-legacy wireless LAN signal. An additional subcarrier may beused without interference of an adjacent bandwidth in the non-legacywireless LAN system with the development of a filter or an amplifierused in the terminal. Referring to FIG. 17, the subcarrier of thenon-legacy wireless LAN signal according to the embodiment of thepresent invention may be configured to include a first subcarrier set800 and a second subcarrier set 820. In more detail, the firstsubcarrier set 800 may be configured equivalent to the subcarrier set ofthe legacy wireless LAN signal illustrated in FIG. 16. Further, thesecond subcarrier set 820 as a subcarrier set different from the firstsubcarrier set 800 may include 4 extra subcarriers, two at each higherand lower indices of the first subcarrier set 800, according to anembodiment. According to the embodiment of FIG. 17, since the non-legacywireless LAN signal uses pilot subcarriers at the same location and ofthe same number as the legacy wireless LAN signal, 52 data subcarrierswhich increase from the existing 48 subcarriers by 4 may be used.According to an embodiment, the subcarrier configuration may be usedafter a legacy preamble part of the non-legacy wireless LAN signal. Thenon-legacy terminal may obtain information through a total of 56subcarriers in the respective non-legacy preamble and data field of thereceived non-legacy wireless LAN signal.

According to the embodiment of the present invention, the secondsubcarrier set 820 included in the non-legacy preamble may represent theBSS identifier information, the bandwidth information of the system, thenon-legacy wireless LAN system information, the channel information, andthe like. In this case, a separate parity bit for parity check of thesecond subcarrier set 820 may be included in the non-legacy preamble.According to an embodiment, when the non-legacy preamble includes therepeated L-SIG field as described above, the BSS identifier information,the bandwidth information of the system, the non-legacy wireless LANsystem information, the channel information, and the like may berepresented through the second subcarrier set 820 of the repeated L-SIGfield.

Meanwhile, according to another embodiment of the present invention, thesubcarrier configuration of FIG. 17 may be extensively applied to thelegacy preamble of the non-legacy wireless LAN signal. That is, thelegacy preamble of the non-legacy wireless LAN signal may additionallyinclude the second subcarrier set 820 and transfer the non-legacywireless LAN information through the second subcarrier set 820. In thiscase, the legacy terminal may not obtain information from the secondsubcarrier set 820, but the non-legacy terminal may obtain additionalinformation from the second subcarrier set 820 of the legacy preamble.

For example, when it is assumed that the second subcarrier set 820additionally used in the legacy preamble includes 4 subcarriers, theindices (that is, subcarrier numbers) of the corresponding subcarriersmay be set to −28, −27, 27, and 28, respectively as illustrated in FIG.17. In this case, when a BPSK modulation scheme is used in the legacypreamble and the same modulation scheme is applied to the secondsubcarrier set, information of a total of 4 bits may be additionallytransmitted. Similarly, when a QPSK modulation scheme is applied to thesecond subcarrier set, information of a total of 8 bits may beadditionally transmitted. In this case, the parity bit for parity checkof the second subcarrier set included in the legacy preamble may beincluded in the non-legacy preamble.

According to an additional embodiment of the present invention, onlysome of total bits which may be represented by the second subcarrier set820 of the legacy preamble may be used for transmitting the additionalinformation. For example, only some bits of the second subcarrier set820 may be used for transmitting the additional information forcompatibility with the parity check of the legacy preamble. That is, theinformation added to the second subcarrier set 820 may be configured tohave even parities for compatibility with the parity bit used in theexisting L-SIG and when the BPSK modulation scheme is used, informationwhich may be transferred through the second subcarrier set 820 may beinformation of a total of 3 bits such as 1010, 0101, 1100, 0011, 1001,0110, 1111, and 0000.

According to another embodiment, a specific bit of the second subcarrierset 820 may be used as the parity check bit and the residual bits may beused for transmitting the additional information. For example, 3 bitsamong 4 bits of the second subcarrier set 820 may be used fortransmitting the additional information and 1 bit may be used as theparity bit. In this case, the parity bit of the second subcarrier set820 may be used for the parity check for bits added by the secondsubcarrier set 820 or otherwise used for parity check of the entireL-SIG including the second subcarrier set 820. In this case, the paritycheck with respect to the legacy wireless LAN signal may be performed byusing the existing parity bit of the L-SIG and the parity check withrespect to the non-legacy wireless LAN signal is performed by using boththe existing parity bit of the L-SIG and the parity bit of the secondsubcarrier set 820 to achieve parity check with higher-reliability.According to yet another embodiment, the parity check with respect tothe non-legacy wireless LAN information added by the second subcarrierset 820 may be performed by using a reserved bit of the L-SIG.

When the additional information for the non-legacy terminal istransmitted through the second subcarrier set 820 of the legacypreamble, the non-legacy terminal may more rapidly obtain the additionalinformation in the legacy preamble of the received wireless LAN signal,thus an initial access delay or detection of a preamble, a header, and apacket which are not required may be reduced by using the obtainedadditional information. Further, according to the embodiment of thepresent invention, the non-legacy terminal may obtain the non-legacywireless LAN information from the second subcarrier set 820 of thelegacy preamble and the non-legacy wireless LAN information obtained inthat case may include the BSS identifier information, the bandwidthinformation of the system, the non-legacy wireless LAN systeminformation, the channel information, and the like. When the non-legacyterminal obtains the second subcarrier set 820 in the legacy preamble ofthe received wireless LAN signal, the non-legacy terminal may recognizethat the corresponding wireless LAN signal includes the non-legacywireless LAN information.

In the embodiment of FIG. 17, the embodiment in which 4 additional datasubcarriers are included in the second subcarrier set 820 is described,but the present invention is not limited thereto and different numbersof subcarriers may be included in a second subcarrier set 820. Further,the embodiment of FIG. 17 may be applied to a case where otherbandwidths including 40 MHz, 80 MHz, and 160 MHz are used as well as acase where a bandwidth of the wireless LAN signal is 20 MHz.

FIG. 18 as yet another embodiment illustrates a method for representingthe non-legacy wireless LAN information by using a predetermined bitfield of the legacy preamble.

According to an additional embodiment of the present invention, thenon-legacy wireless LAN information may be extracted from thepredetermined bit field of the legacy preamble under a specificcondition. FIG. 18 as an embodiment thereof illustrates a rate bit fieldincluded in the L-SIG of the legacy preamble. As illustrated in FIG. 18,a 4-th bit in the rate bit filed of the existing legacy preamble iscontinuously set to 1. Therefore, information on a data rate, amodulation scheme, and a coding rate of the legacy wireless LAN signalmay be obtained through former 3 bit values in the rate bit field.Accordingly, according to the embodiment of the present invention,whether the corresponding rate bit field represents the non-legacywireless LAN information may be decided based on the 4-th bit value ofthe rate bit field. That is, when the 4-th bit of the rate bit field hasa value of 1, the corresponding rate bit field may represent theexisting information, that is, the data rate, the modulation scheme, andthe coding rate. However, when the 4-th bit of the rate bit field has avalue of 0, the corresponding rate bit field may represent thenon-legacy wireless LAN information.

When it is determined that the rate bit field includes the non-legacywireless LAN information, the BSS identifier information may beextracted from former 3 bit values of the corresponding rate bit fieldas illustrated in FIG. 18. However, the present invention is not limitedthereto and the non-legacy wireless LAN information such as bandwidthinformation, channel information, an association identifier (AID), andthe like of the non-legacy wireless LAN signal may be extracted from therate bit field. In this case, actual rate information for the non-legacyterminal may be transmitted through the non-legacy preamble. Meanwhile,even when the rate bit field includes the non-legacy wireless LANinformation, the legacy terminal may analyze the non-legacy wireless LANinformation as rate information. For such a situation, by appropriatelyconfiguring a length field of the L-SIG, the legacy terminals mayperform a transmission delay (NAV configuration, and the like) by usingL-SIG length information of other terminal packets when the transmissiondelay is required due to transmission of other terminals. In moredetail, since the length field of the legacy preamble represents thesize (the number of bytes) of transmission data, when information on thenumber of transmitted bits per OFDM symbol is obtained based on amodulation and coding scheme (MCS) and the length field is divided bythe obtained information, the number of required OFDM symbols isdetermined. In this case, the network allocation vector (NAV)configuration may be performed according to the obtained number of OFDMsymbols, and when the rate bit field is used as the non-legacy wirelessLAN information in accordance with the embodiment of the presentinvention, the NAV may be configured as large as a required length byadjusting the length field.

As such, according to the embodiment of the present invention, based oninformation on predetermined specific bits of the legacy preamble,whether the corresponding legacy preamble includes the non-legacywireless LAN information may be determined. When it is determined thatthe legacy preamble includes the non-legacy wireless LAN information,the non-legacy wireless LAN information such as the BSS identifierinformation, and the like may be extracted from the predetermined bitfield of the legacy preamble, for instance, the rate bit field.

Meanwhile, according to an additional embodiment of the presentinvention, information on more bits may be secured by using acombination of the second subcarrier set of the legacy preamble and thespecific bit field (that is, rate bit field), and as a result, thenon-legacy wireless LAN information may be transferred. For example,when the legacy preamble is configured to additionally include thesecond subcarrier set, the non-legacy terminal may determine that thecorresponding legacy preamble includes the non-legacy wireless LANinformation and extract the BSS identifier information from all or someof 4 bits in the rate bit field. Furthermore, when the legacy preambleis configured to additionally include the second subcarrier set, thenon-legacy terminal may analyze the entirety of the L-SIG bit field ofthe legacy preamble as the non-legacy wireless LAN information. As such,according to the embodiment of FIG. 18, since at least some ofnon-legacy wireless LAN information such as the BSS identifierinformation, and the like may be obtained from the legacy preamblebefore checking the non-legacy preamble, the CCA may be performed withina shorter time.

FIG. 19 illustrates an embodiment of the present invention fortransmitting and receiving data between a non-legacy terminal and alegacy terminal. In the embodiment of FIG. 19, ax_AP and ax_STArepresent a non-legacy AP and a non-legacy STA, respectively. Also,legacy_AP and legacy_STA represent a legacy_AP and a legacy_STA thatsupport legacy WLAN standards (e.g., 802.11a/g/n/ac standards),respectively. According to the embodiment of the present invention, awireless LAN signal in the legacy frame format can be transmitted notonly by the legacy terminals but also by the non-legacy terminals. Thatis, the non-legacy terminal can transmit the wireless LAN signal in thelegacy frame format when transmitting the signal to the legacy terminal.

FIG. 19 (a) and 19 (b) illustrate an embodiment that a non-legacy AP ‘A’and a non-legacy STA ‘A-1’ constitute one BSS and a non-legacy AP ‘B’, alegacy STA ‘B-1’ and a non-legacy STA ‘B-2’ constitute another BSS.

First, according to the embodiment of FIG. 19 (a), the non-legacy AP ‘B’transmits a wireless LAN signal in the legacy frame format to the legacySTA ‘B-1’. According to an embodiment, non-legacy wireless LANinformation may be included in the wireless LAN signal in the legacyframe format transmitted by the non-legacy terminal. In this case, thenon-legacy wireless LAN information may include BSS color information.The BSS color information may represent abbreviated information of theBSS identifier or information of a predetermined type for distinguishingdifferent BSSs. The non-legacy terminals extract the BSS colorinformation from the wireless LAN signal in the legacy frame format andperform the CCA based on the extracted BSS color information. Morespecifically, the terminals ‘A’ and ‘A-1’ may identify the correspondingwireless LAN signal to be a wireless signal of the other BSS (i.e.,OBSS) based on the extracted BSS color information, and may perform theCCA based on the aforementioned second CCA threshold (i.e., the secondCCA-SD threshold). In addition, the terminal B-2 may identify thecorresponding wireless LAN signal to be the wireless LAN signal of thesame BSS (i.e., MYBSS) based on the extracted BSS color information, andmay perform the CCA based on the first CCA threshold (i.e., the firstCCA-SD threshold).

However, when the legacy STA ‘B-1’ transmits the WLAN signal in thelegacy frame format to the non-legacy AP ‘B’ as in the embodiment ofFIG. 19 (b), the BSS color information is not included in thecorresponding signal. Therefore, the terminals receiving the legacywireless LAN signal may perform the CCA using only the signal strengthinformation of the corresponding signal.

Next, FIGS. 19 (c) and 19 (d) illustrate an embodiment that anon-legacy_AP ‘A’ and a non-legacy STA ‘A-1’ constitute one BSS and alegacy AP ‘B’, a non-legacy STAs ‘B-1’ and ‘B-2’ constitute another BSS.According to the embodiment of FIG. 19 (c), the wireless LAN signal inthe legacy frame format transmitted by the legacy AP ‘B’ does notinclude BSS color information. Therefore, terminals receiving the legacywireless LAN signal may perform the CCA using only the signal strengthinformation of the corresponding signal. However, when the non-legacySTA ‘B-1’ transmits the wireless LAN signal in the legacy frame formatto the legacy AP ‘B’ as in the embodiment of FIG. 19 (d), the BSS colorinformation may be included in the corresponding signal. Accordingly,non-legacy terminals receiving the corresponding signal may extract theBSS color information from the corresponding signal and perform the CCAbased on the extracted BSS color information, as described above withreference to FIG. 19 (a).

According to an embodiment of the present invention, BSS identifierinformation may be included in the corresponding signal even when alegacy wireless LAN signal is transmitted, and the non-legacy terminalmay adjust the CCA threshold based on the BSS identifier informationextracted from the corresponding signal. In this case, when thecorresponding signal is a wireless LAN signal of the same BSS (i.e.,MYBSS), the non-legacy terminal performs the CCA based on thepredetermined first CCA threshold. However, when the correspondingsignal is a wireless LAN signal of another BSS (i.e., OBSS), thenon-legacy terminal performs the CCA based on a predetermined second CCAthreshold higher than the first CCA threshold.

FIG. 20 illustrates a further embodiment of a CCA method according tothe present invention. In the embodiment of FIG. 20, duplicativedescription of parts, which are the same as or correspond to theaforementioned embodiments of FIGS. 8 to 13, will be omitted.

According to a further embodiment of the present invention, a legacywireless LAN signal, i.e. a wireless LAN signal having a legacy frameformat, can be further classified. The wireless LAN signal having thelegacy frame format may include the BSS identifier information. Here,the BSS identifier information includes the BSS identifier itself or theabbreviated information of the identifier (i.e., BSS color). Accordingto an exemplary embodiment, the wireless LAN signal having the legacyframe format may indicate BSS identifier information through separatenon-legacy wireless LAN information. According to another embodiment,the wireless LAN signal having the legacy frame format may indicate BSSidentifier information through MAC address information included in atleast one field of a MAC header. The wireless LAN signal having thelegacy frame format may include the MAC address of the AP in at leastone of a transmitter address (TA) and a receiver address (RA) of the MACheader, whereby the BSS identifier information of the correspondingsignal can be extracted. However, in the case of a frame in apredetermined format (e.g., a legacy CTS frame, a legacy ACK frame,etc.) in which the MAC address of the AP is not included in the MACheader, the BSS identifier information may not be extracted from thecorresponding signal.

In the embodiment of FIG. 20, the wireless signal 543 represents alegacy wireless LAN signal of another BSS (i.e., OBSS) from which BSSidentifier information is extracted, and the wireless signal 544represents a legacy wireless LAN signal of another BSS (i.e., OBSS) fromwhich BSS identifier information is not extracted. In addition, thewireless signal 546 represents a legacy wireless LAN signal of the sameBSS (i.e., MYBSS) from which BSS identifier information is notextracted, and the wireless signal 547 represents a legacy wireless LANsignal of the same BSS (i.e., MYBSS) from which BSS identifierinformation is extracted.

The legacy WLAN signals 543 and 547 from which BSS identifierinformation is extracted may include the BSS identifier informationaccording to various embodiments. As described above, the correspondingsignal may include the BSS identifier information through separatenon-legacy wireless LAN information. Alternatively, the correspondingsignal may include the BSS identifier information through MAC addressinformation included in at least one field of the MAC header. Meanwhile,the legacy wireless LAN signals 544 and 546 in the predetermined frameformat from which the BSS identifier information is not extracted do notinclude the non-legacy wireless LAN information and do not include theBSS identifier information in the MAC header. According to anembodiment, the wireless LAN signals 544 and 546 may include a legacyCTS frame, a legacy ACK frame, and the like, but the present inventionis not limited thereto.

Referring to FIG. 20, when the received signal strength RX RSSI of thereceived wireless signal of a specific channel is the RX sensitivity 50or more and the first CCA-SD threshold 40 or less, the correspondingchannel is determined to be idle. When the received signal strength RXRSSI of the received wireless signal of the specific channel is higherthan the first CCA-SD threshold 40, the terminal adjusts the CCAthreshold according to whether the wireless signal is a wireless LANsignal of the same BSS as the corresponding terminal.

First, when the received wireless signal is identified to be a wirelessLAN signal of another BSS (i.e., OBSS), the terminal adjusts thethreshold for performing CCA to the second CCA-SD threshold 20 andperforms the CCA using the second CCA-SD threshold 20. Morespecifically, the cases in which a received wireless signal isidentified to be the wireless LAN signal of another BSS (i.e., OBSS) areas follows. i) In case that the received wireless signal 542 includesnon-legacy wireless LAN information, and BSS identifier informationextracted from the non-legacy wireless LAN information indicates adifferent BSS from that of the corresponding terminal. ii) In case thatthe received wireless signal 543 has the legacy frame format butincludes the BSS identifier information, and the BSS identifierinformation indicating the same BSS as that of the correspondingterminal is not extracted from the corresponding signal 543. At thistime, in the case ii), the wireless signal 543 may indicate the BSSidentifier information through the MAC address included in the MACheader. If the signal strength of the received wireless signal is higherthan the second CCA-SD threshold 20, the terminal determines that thechannel is busy. However, if the signal strength of the receivedwireless signal is lower than the second CCA-SD threshold 20, theterminal determines that the channel is idle.

On the other hand, when the received wireless signal is identified to bea wireless LAN signal of the same BSS (i.e., MYBSS), the terminalperforms CCA using the first CCA-SD threshold 40 without changing thethreshold for performing the CCA. More specifically, the cases in whicha received wireless signal is identified to be the wireless LAN signalof the same BSS (i.e., MYBSS) are as follows. i) In case that thereceived wireless signal 548 includes non-legacy wireless LANinformation, and BSS identifier information extracted from thenon-legacy wireless LAN information indicates the same BSS as that ofthe corresponding terminal. ii) In case that the received wirelesssignal 547 has the legacy frame format but includes the BSS identifierinformation, and the BSS identifier information indicating the same BSSas that of the corresponding terminal is extracted from thecorresponding signal 547. At this time, in the case ii), the wirelesssignal 547 may indicate the BSS identifier information through the MACaddress included in the MAC header. iii) In case that the receivedwireless signals 544 and 546 are legacy wireless LAN signals in apredetermined frame format that do not have the BSS identifierinformation. According to an embodiment, the wireless signals 544 and546 in case iii) include a legacy CTS frame, a legacy ACK frame, and thelike. In this case, since the signal strength of the received wirelesssignal is higher than the first CCA-SD threshold 20, the terminaldetermines that the channel is busy.

FIGS. 21 to 25 illustrate various embodiments of the present inventionin which a wireless communication terminal performs the backoffprocedure to transmit data. According to the embodiment of the presentinvention, the terminal may perform the backoff procedure using thefirst CCA threshold or the second CCA threshold determined according tothe aforementioned embodiments.

As described with reference to FIG. 5, a terminal which intends totransmit data performs a backoff procedure 80 a predetermined IFS time(e.g., 1st AIFS) after a channel becomes idle. In this case, the backoffprocedure 80 is performed based on the first CCA threshold. If awireless signal 600 having a signal strength higher than a predeterminedfirst CCA threshold is received through the corresponding channel, theterminal suspends the backoff procedure 80 and identifies whether thecorresponding signal 600 is a wireless signal of the same BSS as that ofthe terminal. Whether it is the wireless signal of the same BSS as thatof the terminal is identified based on the BSS identifier informationextracted from the corresponding signal 600. According to an embodimentof the present invention, the BSS identifier information may beextracted from any one of i) a non-legacy preamble, ii) non-legacywireless LAN information of a legacy preamble, and iii) a MAC address ofa MAC header of the wireless signal.

The terminal determines whether to resume the backoff procedure based onthe CCA threshold determined according to the identification result. Ifit is identified that the received wireless signal 600 is a wirelesssignal of a different BSS with the terminal, the terminal determineswhether to resume the backoff procedure using the second CCA thresholdhigher than the first CCA threshold. Hereinafter, the embodiments ofFIGS. 21 to 25 will be described on the assumption that the backoffcounter of the terminal is set to 3.

FIG. 21 illustrates an embodiment in which the BSS identifierinformation is extracted from the non-legacy preamble of the wirelesssignal 600. According to an embodiment of the present invention, thewireless signal 600 may include BSS color information in a predeterminedfield of a non-legacy preamble, such as non-legacy SIG-A. When the BSScolor information is extracted, the terminal identifies whether thecorresponding wireless signal 600 is a wireless signal of the same BSSas the terminal with reference to the extracted BSS color information.If the corresponding signal 600 is identified to be a wireless signal ofa different BSS with the terminal, the terminal determines whether toresume the backoff procedure using the second CCA threshold higher thanthe first CCA threshold. When the signal strength of the correspondingsignal 600 is higher than the second CCA threshold, the terminaldetermines that the channel is busy and continues to suspend the backoffprocedure 80. However, when the signal strength of the correspondingsignal 600 is lower than the second CCA threshold, the terminaldetermines that the channel is idle and resumes the backoff procedure80′ after a predetermined IFS time (i.e., 2nd AIFS). In this case, thepredetermined IFS may be an AIFS. The resumed backoff procedure 80′ isperformed using a remaining backoff counter in the previous backoffprocedure 80. When the backoff counter of the backoff procedure 80′expires, the terminal transmits data 620.

FIG. 22 illustrates an embodiment in which the BSS identifierinformation is extracted from the legacy preamble of the wireless signal600. According to another embodiment of the present invention, thewireless signal 600 may indicate the BSS identifier information throughadditional information of the legacy preamble. A specific embodiment isas illustrated in FIGS. 14 to 18. When the BSS identifier information isincluded in the legacy preamble of the wireless signal 600, the BSSidentifier information may be extracted from the wireless signal 600 ina short period of time. According to an embodiment, the BSS identifierinformation may be extracted within one slot period after the wirelesssignal 600 is received.

When the BSS identifier information is extracted, the terminalidentifies whether the corresponding wireless signal 600 is a wirelesssignal of the same BSS as the terminal by referring to the extracted BSSidentifier information. If the corresponding signal 600 is determined tobe a wireless signal of a different BSS with the terminal, the terminaldetermines whether to resume the backoff procedure using the second CCAthreshold higher than the first CCA threshold. When the signal strengthof the corresponding signal 600 is higher than the second CCA threshold,the terminal determines that the channel is busy and continues tosuspend the backoff procedure 80. However, when the signal strength ofthe corresponding signal 600 is lower than the second CCA threshold, theterminal determines that the channel is idle and resumes the backoffprocedure.

However, if the previous backoff procedure 80 is resumed and the data620 is transmitted immediately after the BSS identifier information ofthe wireless signal 600 is identified, the preamble portion of thewireless signal 600 and the transmitted data 620 signal of the terminalmay collide with each other. Since the preamble of the wireless signal600 includes important information necessary for receiving the data ofthe corresponding signal, a method for protecting the preamble isneeded. Therefore, according to the embodiment of the present invention,the terminal performs an extended backoff procedure 82 after identifyingthe BSS identifier information of the wireless signal 600 to delay thetransmission of the data 620 until the preamble transmission of thewireless signal 600 is completed.

The backoff counter of the extended backoff procedure 82 may be set to areserved value or may be set based on the remaining time until thepreamble transmission of the wireless signal 600 is completed. In theembodiment of FIG. 22, an extended backoff procedure 82 in which abackoff counter 5 is assigned is shown. When the extended backoffprocedure 82 is terminated, the terminal transmits data 620. Meanwhile,if the transmission of the data 620 of the terminal is further delayeddue to the extended backoff procedure 82, compensation for the nextround channel access of the terminal may be performed. That is, in thenext round channel access, the terminal may perform a backoff procedureusing a counter obtained by subtracting the backoff counter used in theprevious extended backoff procedure 82 from a randomly selected backoffcounter in the corresponding round.

Meanwhile, if the preamble transmission of the wireless signal 600 isnot completed until the resumed backoff procedure 80′ is terminated inthe embodiment of FIG. 21, the terminal may additionally perform theextended backoff procedure 82 as in the embodiment of FIG. 22.

FIGS. 23 to 25 illustrate modified embodiments of the embodiments ofFIGS. 21 and 22. In the embodiments of FIGS. 23 to 25, duplicativedescription of parts, which are the same as or correspond to theaforementioned embodiments of FIGS. 21 and 22, will be omitted.

First, according to the embodiment of FIG. 23, the terminal may resumethe backoff procedure 80′ after identifying the BSS identifierinformation of the wireless signal 600, and may delay the transmissionof data 620 by performing the extended backoff procedure when theresumed backoff procedure 80′ is terminated. The resumed backoffprocedure 80′ is performed using a remaining backoff counter in theprevious backoff procedure 80. When the resumed backoff procedure 80′ isterminated, the terminal immediately performs the extended backoffprocedure 82. The backoff counter used in the extended backoff procedure82 may be determined as described in the embodiment of FIG. 22, and whenthe extended backoff procedure 82 is terminated, the terminal transmitsdata 620.

Next, according to the embodiment of FIG. 24, the terminal may resumethe backoff procedure 80′ a predetermined IFS time (i.e., 2nd AIFS)after identifying the BSS identifier information of the wireless signal600. In this case, the predetermined IFS may be an AIFS. When thebackoff counter of the backoff procedure 80′ expires, the terminaltransmits data 620.

Next, according to the embodiment of FIG. 25, the terminal may resumethe backoff procedure 80′ a predetermined IFS time (i.e., 2nd AIFS)after identifying the BSS identifier information of the wireless signal600, and may perform the extended backoff procedure 82 when the resumedbackoff procedure 80′ us terminated to delay the transmission of thedata 620. A specific embodiment of the resumed backoff procedure 80′ andthe extended backoff procedure 82 is as described above. When theextended backoff procedure 82 is terminated, the terminal transmits data620.

Meanwhile, in the embodiments of FIGS. 21 to 25, when the receivedsignal 600 is identified to be a wireless signal of the same BSS as theterminal, the terminal performs the CCA by using the first CCA thresholdwithout changing the threshold for performing the CCA. Therefore, theterminal determines that the channel is busy and continues to suspendthe backoff procedure 80. In addition, FIGS. 21 to 25 illustrateembodiments in which the BSS identifier information is included in thenon-legacy preamble of the wireless signal 600 or the non-legacywireless LAN information of the legacy preamble of the wireless signal600. However, as described above, the BSS identifier information may beincluded in the MAC header as MAC address information, or may beincluded in the wireless signal 600 in other forms.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

MODE FOR INVENTION

As above, related features have been described in the best mode.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1. A wireless communication terminal comprising: a transceiverconfigured to transmit and receive a wireless signal; and a processorconfigured to control an operation of the terminal, wherein theprocessor is configured to: perform a backoff procedure of a channel fordata transmission, suspend the backoff procedure when a wireless signalhaving a signal strength higher than a predetermined first clear channelassessment (CCA) threshold is received through the channel, identifywhether the received wireless signal is a wireless signal of the samebasic service set (BSS) as the terminal, and determine whether to resumethe backoff procedure based on a CCA threshold determined according tothe identification result.
 2. The terminal of claim 1, wherein theprocessor is further configured to: determine whether to resume thebackoff procedure using a second CCA threshold higher than the first CCAthreshold when the wireless signal is determined to be a wireless signalof a different BSS with the terminal.
 3. The terminal of claim 2,wherein the processor is further configured to: determine that thechannel is busy and continue to suspend the backoff procedure when thesignal strength of the wireless signal is higher than the second CCAthreshold.
 4. The terminal of claim 2, wherein the processor is furtherconfigured to: determine that the channel is idle and resume the backoffprocedure after a predetermined IFS time when the signal strength of thewireless signal is lower than the second CCA threshold.
 5. The terminalof claim 1, wherein whether the received wireless signal is a wirelesssignal of the same BSS as the terminal is identified based on BSS colorinformation or MAC address information extracted from the wirelesssignal.
 6. The terminal of claim 5, wherein the BSS color information isabbreviated information of a BSS identifier.
 7. The terminal of claim 1,wherein when the wireless signal is a wireless LAN signal in a legacyframe format, the wireless signal includes BSS color information, andwherein the processor extracts BSS color information from the wirelesssignal in a legacy frame format and identifies whether the receivedwireless signal is a wireless signal of the same BSS as the terminalbased on the extracted BSS color information. The terminal of claim 1,wherein the wireless signal is identified to be a wireless signal of thesame BSS as the terminal when the wireless signal is a frame of apredetermined format not including the BSS identifier information. 8.The terminal of claim 1, wherein when the wireless signal is a legacywireless LAN signal in a predetermined frame format, the processordetermines whether to resume the backoff procedure based on the firstCCA threshold. The terminal of claim 7, wherein the frame of thepredetermined format includes a legacy CTS frame.
 9. The terminal ofclaim 1, wherein the processor is further configured to: determine thatthe channel is busy and continue to suspend the backoff procedure whenthe wireless signal is identified to be a wireless signal of the sameBSS as the terminal.
 10. A wireless communication method of a terminal,the method comprising: performing a backoff procedure of a channel fordata transmission; suspending the backoff procedure when a wirelesssignal having a signal strength higher than a predetermined first clearchannel assessment (CCA) threshold is received through the channel;identifying whether the received wireless signal is a wireless signal ofthe same basic service set (BSS) as the terminal; and determiningwhether to resume the backoff procedure based on a CCA thresholddetermined according to the identification result.
 11. The method ofclaim 10, wherein the determining step determines whether to resume thebackoff procedure using a second CCA threshold higher than the first CCAthreshold when the wireless signal is determined to be a wireless signalof a different BSS with the terminal.
 12. The method of claim 11,wherein the determining step determines that the channel is busy andcontinues to suspend the backoff procedure when the signal strength ofthe wireless signal is higher than the second CCA threshold.
 13. Themethod of claim 11, wherein the determining step determines that thechannel is idle and resumes the backoff procedure after a predeterminedIFS time when the signal strength of the wireless signal is lower thanthe second CCA threshold.
 14. The method of claim 10, wherein whetherthe received wireless signal is a wireless signal of the same BSS as theterminal is identified based on BSS color information or MAC addressinformation extracted from the wireless signal.
 15. The method of claim14, wherein the BSS color information is abbreviated information of aBSS identifier.
 16. The method of claim 10, wherein when the wirelesssignal is a wireless LAN signal in a legacy frame format, the wirelesssignal includes BSS color information, and wherein the identifying stepextracts BSS color information from the wireless signal in a legacyframe format and identifies whether the received wireless signal is awireless signal of the same BSS as the terminal based on the extractedBSS color information.
 17. The method of claim 10, wherein when thewireless signal is a legacy wireless LAN signal in a predetermined frameformat, the determining step determines whether to resume the backoffprocedure based on the first CCA threshold.
 18. The method of claim 10,wherein the determining step determines that the channel is busy andcontinues to suspend the backoff procedure when the wireless signal isidentified to be a wireless signal of the same BSS as the terminal.